Several trends presently exist in the semiconductor and electronics industry. One of these trends is that recent generations of portable electronic devices are using more memory than previous generations. This increase in memory allows these new devices to store more data, such as music or images, and also provides the devices with more computational power and speed.
One type of non-volatile memory that has recently been developed is called resistive or resistively switched memory devices. In such a resistive memory, a memory material positioned between two appropriate electrodes (i.e., an anode and a cathode) is placed, by appropriate switching processes, in a more or less conductive state, wherein the more conductive state corresponds to a logic “1”, and the less conductive state corresponds to a logic “0” (or vice versa). Suitable resistive memories can be, for example, perovskite memory, as described in W. W. Zhuang et al., “Novel Colossal Magnetoresistive Thin Film Nonvolatile Resistance Random Access Memory (RRAM)”, IEDM 2002, resistive switching in binary oxides (OxRAM), for example, as described in I. G. Baek et. al., “Multi-layer crosspoint binary oxide resistive memory (OxRAM) for post-NAND storage application”, IEDM 2005, phase change memory (PCRAM), and conductive bridging RAM (CBRAM).
In the case of phase change memory, an appropriate chalcogenide compound (e.g., a GeSbTe or an AginSbTe compound) may, for instance, be used as the active material that is positioned between the two corresponding electrodes. The chalcogenide compound material can be placed in an amorphous, i.e., relatively weakly conductive, or a crystalline, i.e., relatively strongly conductive state by means of appropriate switching processes, and thus behaves like a variable resistance element, which as highlighted above, may be exploited as differing data states.
In order to achieve a change in the phase change material from an amorphous state to a crystalline state, an appropriate heating current is applied to the electrodes, wherein the current heats the phase change material beyond the crystallization temperature thereof. This operation is sometimes called a SET operation. Similarly, a change of state from a crystalline state to an amorphous state is achieved by application of an appropriate heating current pulse, wherein the phase change material is heated beyond the melting temperature thereof, and the amorphous state is obtained during the rapid cooling process thereof. This operation is sometimes called a RESET operation. The combination of SET and RESET operations is one means by which data can be written to a phase change memory cell. Reading these SET and RESET data states is sometimes called a read operation.